[ skip to content ]

Fall 2010

Schedule Fall 2010

Tuesday September 14, 2010

"Exploring Hypersonic Flow Using Laser Spectroscopy"


Dr. Paul Danehy

NASA

Laser-spectroscopic imaging methods can provide high-quality visualizations of planar slices in hypersonic flows and measure parameters like temperature, velocity, pressure and gas composition without disturbing the flow itself. NASA is developing a method for 2D and 3D imaging of hypersonic flows, called Nitric Oxide Planar Laser-Induced Fluorescence (NO-PLIF). NO-PLIF has been used to study basic transition flow physics relevant to transition control for scramjet engine inlets. It has also been used to study the effects of reaction control system jets, shear layers, wake flowfields, and simulated heat-shield ablation related to high mass Mars entry technology. Additionally, NO PLIF has been used to study the Orion Crew Exploration Vehicle. Moreover, experiments motivated by the Shuttle Return-to-Flight program have included visualizations of flow transition over simulated gap fillers and a detailed study of the breach of the orbiter's wing leading edge. Quantitative measurements using a point-wise technique called Coherent Anti-Stokes Raman Spectroscopy (CARS) have been used to study supersonic combustion flows applicable to scramjet engines. CARS measures temperature and composition and can be used even in ducted engines with limited optical access. Such measurements are useful for testing and developing new computational models for predicting supersonic combustion. This talk will describe the use and application of two laser-based spectroscopic measurement (NO PLIF, and CARS) techniques to study hypersonic flows and supersonic combustion


Tuesday September 21, 2010

"CritRHIC: The Search For The Nuclear Phase Diagram Critical Point At RHIC"


Dr. Todd Satogata

Jefferson Lab

Significant evidence points to the existence of a phase transition critical point on the QCD phase diagram. Experimental identification of this critical point would be a major step in understanding nuclear phase transitions. If this critical point exists, it should appear in a range of RHIC collision cm energies from sqrt(s_NN)=5-50 GeV/u. The lowest part of this range is over a factor of four below RHIC design injection energy. This talk will review RHIC experience and challenges for low energy operations, including harmonic number changes, reduced field quality, nonlinear orbit control, luminosity monitoring, and potential cooling upgrades. I will also discuss experience with first RHIC operations at sqrt(s_NN)=7.7 GeV/u and
11.5 GeV/u in early 2010.


Tuesday October 19, 2010

"Orbits in Superconducting RF Cavities: A Challenge for Established Physics"


Dr. David Fryberger

Stanford Linear Accelerator Center

A number of data runs have been performed at TJNAF by the ALE Collaboration (with membership from TJNAF and SLAC). These runs were to study anomalous light emissions generated in the interior of high vacuum superconducting cavities (at 2 K) under (1.5 GHz) RF excitation. These light emissions and their associated phenomena were observed by a small monochrome video camera, looking through a standard optical viewport, as well as by other instrumentation. Of the several phenomena observed, the most perplexing are what appear to be small luminous long-lived objects moving about in the vacuum space in the interior of the cavities without wall contact. In our several runs, more than a dozen (closed) orbits of these Mobile Luminous Objects (or MLOs) were observed, five of which lasted longer than 10 s. These orbits were often elliptical or near elliptical. Orbital frequencies ranged from 5 to 80 Hz. Perhaps the most spectacular orbit, taken on the last run, orbited for ~40 s (at ~40 Hz) about the cavity axis. By using reflections in the wall of the cavity beam tube it is be shown that the trajectory of this 40 s orbit was in, or near, the equatorial plane of the cavity and did not contact the cavity walls. A most intriguing feature of this orbit was a combination of orbital precession and rocking motion (spanning about 70°) having a rocking period of about 5s.

Of the various anomalous luminous phenomena in the data, these long-lived orbiting MLOs present the greatest challenge to theoretical explanation. To proceed with an analysis, the MLO physics is partitioned into internal and external. While the internal physics is as of yet unknown, an analysis of the external physics, that is the MLO orbits, is straightforward.

Using the data as a guide, it is argued that the MLOs are coherent entities of small size (£ 2 mm) and carry a certain mass. Thus, one expects them to obey Newton's equations. Then, MLO models are formulated by characterizing these (small) entities by various electromagnetic features (charges, dipoles, etc.) that can interact with the cavity environment. It is observed that one does not have to understand the internal MLO dynamics that lead to these assumed electromagnetic features; given the specified electromagnetic features of the (model) MLOs, the analysis of the external MLO dynamics will still be valid.

Based upon the character of the experimentally observed orbits, five criteria are developed that a satisfactory theoretical explanation for the MLO orbits would have to successfully address. A number of model MLOs are analyzed in detail. Some models are more successful than others, but it is shown that none of the models that are considered have a viable parameter space that can accommodate all five of the orbital criteria. It is further argued that the set of models analyzed herein exhausts the plausible MLO modeling possibilities available from the realm of established physics. This line of argument leads to a challenging conclusion.


Tuesday November 9, 2010

"Laser Wakefield Acceleration at Low Density in the Blowout Regime"


Dr. Joe Ralph

Lawrence Livermore National Laboratory

NIF/Photon Sciences

In a laser wakefield accelerator, an ultrashort, relativistically intense laser pulse (a0>2) drives an electron plasma wave of sufficient amplitude to trap and accelerate electrons to very high energies in short distances. Such “table-top” accelerators have the potential to bring high-energy, high quality electron beams to universities, hospitals and research facities. Recently, several advances in the theory and simulations of the blowout laser wakefield accelerator regime have produced a model describing the balance between the nonlinear optical effects of self-focusing and local pump depletion. An overview of these advances will be presented with experimental and simulation results. In addition, a review of recent experimental campaigns performed using mixed gas and pure Helium targets ranging in length from 3 mm to 14 mm produced electron energies beyond 700 MeV in a monoenergetic beam and beyond 1.4 GeV in a tail of electrons. To achieve such high-energy electrons, a 200 TW 60 fs laser pulse was focused to a spot size of 15 microns and propagated through underdense plasmas with densities ranging from 1018 to 1019 cm-3. Current experimental work focuses on extending the interaction length and increasing the energy as well as reducing the energy spread of the GeV electrons by combining an injection stage with an acceleration stage. A portion of this work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and a Department of Energy Grant No. DEFG02-92ER40727 and was partially funded by the Laboratory Directed Research and Development Program under tracking code 06-ERD-056.


Tuesday November 16, 2010

"Wave of the Future: Advanced LIGO and the Next Generation of Gravity Wave Detectors"


Dr. Steven Penn

Hobart and William Smith Colleges

The current generation of interferometric gravitational wave observatories have achieved an impressive level of sensitivity in their quest to make the first direct detection of gravity waves. Until recently the LIGO detectors operated at a length sensitivity of 10^-18 m with a detection range of 20 Mpc. Now LIGO is the first of the worldwide network to be shutdown for an upgrade that will increase this sensitivity by a factor 10. We will discuss the design of these next generation detectors, and what we hope to learn about the universe when they become operational


Tuesday November 23, 2010

"Fundamental measurements of the proton’s sub-structure
using high-energy polarized proton-proton collisions"


Dr. Bernd Surrow

Massachusetts Institute of Technology

Understanding the structure of matter in terms of its underlying constituents has a long tradition in science. A key question is how we can understand the properties of the proton, such as its mass, charge, and spin (intrinsic angular momentum) in terms of its underlying constituents: nearly massless quarks (building blocks) and massless gluons (force carriers). The strong force that confines quarks inside the proton leads to the creation of abundant gluons and quark-antiquark pairs (QCD sea). These ‘silent partners’ make the dominant contribution to the mass of the proton. Various polarized deep-inelastic scattering measurements have shown that the spins of all quarks and antiquarks combined account for only 25% of the proton spin.

New experimental techniques are required to deepen our understanding on the role of gluons and the QCD sea to the proton spin. High energy polarized proton-proton (p + p) collisions at RHIC at Brookhaven National Laboratory provide a new and unique way to probe the proton spin structure using very well established processes in high-energy physics, both experimentally and theoretically.

A major new tool has been established for the first time using parity-violating W boson production in polarized p + p collisions at √ s = 500 GeV demonstrating directly the different polarization patterns of different quark flavors, paving the path to study the polarization of the QCD sea. Various results in polarized p + p collisions at √ s = 200 GeV constrain the degree to which gluons are polarized suggesting that the contribution of the gluons to the spin of the proton is rather small, in striking contrast to their role in making up the mass of the proton.


November 30
Dr. Patrick McQuillan, Incorporated Research Institutions for Seismology


December 7

Senior Thesis Presentations